This invention relates to characterising the motion of one or more objects using acoustic signals; particularly, although not exclusively, using ultrasound.
It is known to track finger movements for touchless interaction with a computing device with an ultrasonic transmitter and a number of receivers using time-of-flight measurements. Indeed various proposals for such tracking have been made—e.g. in US patent application US 2006/0161871 by Apple Inc.®, which relates particularly to input to a handheld device. However these proposals have shortcomings. In particular, they can be sensitive to noise caused by changes in the shape or view-angle of the finger, or interference from one or more other objects.
Optical tracking based on time-of-flight principles has also been attempted; however, the technology is complex and costly, due in part to the need for optical components and the very high clock-speeds required. Furthermore, it is impossible to flush-mount a camera having a wide (e.g. 180-degree) field of view, meaning that camera lenses must partly project from the surface of the device so that they are exposed to damage and contamination, as well as being potentially less aesthetically-pleasing.
The disclosed embodiments aim to take a different approach.